The present invention relates to a developer composition for presensitized plates for use in making lithographic printing plates (hereunder referred to as "PS plates") and a method for developing PS plates.
It is known that diazo groups of o-quinonediazide compounds are dissociated by irradiating them with actinic rays and thus the o-quinonediazide compounds are converted to those having carboxylic acid groups. If an imagewise exposed light-sensitive layer containing such an o-quinonediazide compound is developed with an alkaline developer, the exposed portion thereof is removed and the un-exposed portion thereof forms images. Therefore, such o-quinonediazide compounds are recently widely used as so-called positive working light-sensitive components for, in particular, compositions for light-sensitive layers of PS plates or for photoresist compositions for use in etching. Particularly, compositions composed of o-quinonediazide compounds admixed with alkali-soluble resins are favorably used for economical and practical reasons. Among these, those admixed with a novolak type phenol-formaldehyde condensed resin or cresolformaldehyde condensed resin are generally used.
As developers for light-sensitive layers containing these o-quinonediazide compounds, there is used an aqueous solution containing sodium tertiary phosphate, sodium hydroxide, sodium silicate, potassium silicate, ammonium silicate or a mixture thereof. However, aqueous solutions of sodium hydroxide, sodium tertiary phosphate and the like strongly etch metal plates such as aluminum plate and, therefore, they are unfavorable as developers for PS plates in which metal plates are used as substrates, depending on developing time. Moreover, it is difficult to achieve uniform development of PS plates and in the worst case, it is sometimes observed that images are disappeared if developing time is only slightly extended. Moreover, a developer is remarkably deteriorated when it is repeatedly used and thus processability of a constant volume of a developer (i.e., the amount of PS plates which can be processed with such an amount of a developer) is quite low. For this reason, there have rather favorably been used an aqueous solution of sodium silicate or potassium silicate recently. This is because these aqueous solutions have low etching power and the developability thereof can be controlled to some extent by adjusting the concentration of silicon oxide (SiO.sub.2) and sodium oxide (Na.sub.2 O) or potassium oxide (K.sub.2 O) which are components of sodium silicate or potassium silicate and the ratio (SiO.sub.2 /Na.sub.2 O or SiO.sub.2 /K.sub.2 O) (in general expressed in molar ratio). In other words, as the amount of SiO.sub.2 increases, developing power of a developer is suppressed and developing stability thereof is increased, while as the amount of Na.sub.2 O or K.sub.2 O increases, the developing power becomes high and the developing stability is lowered. The term "developing stability" herein used means stability of images as a function of developing time. Thus, if only the amount of Na.sub.2 O or K.sub.2 O increases, images are apt to disappear within a short time period.
Processability of a constant volume of a developer becomes high as the content of Na.sub.2 O or K.sub.2 O increases. Therefore, the developability, stability and processability can be imparted to a developer to some degree by increasing the total concentration while adjusting the ratio: SiO.sub.2 /Na.sub.2 O or SiO.sub.2 /K.sub.2 O as a function of developing power and developing stability. However, these developers do not satisfy these requirements at the same time. More specifically, if a desired level of developing power is established, stability is impaired and if a desired stability is established, developing power and processability would be impaired. In addition, these solutions contain such components in a relatively high concentration. Thus they easily form precipitates and a large amount of an acid is needed to neutralize them in treating waste.
The summary of the problems of the aforementioned developers containing sodium hydroxide, sodium tertiary phosphate, sodium silicate, potassium silicate or the like is as follows: if the strength of alkali is increased, the developing power and processability of the developers are improved, but the developing stability thereof is insufficient. Moreover, the concentration of alkalis must be reduced to achieve developing stability, but this leads to reduction of processability. Thus, high developing stability can be imparted to a developer while maintaining high alkali strength thereof, to obtain excellent developers.
As means for obtaining desired developers having good developing stability while holding high alkali strength, Japanese Patent Unexamined Publication (hereunder referred to as "J. P. KOKAI") No. Sho 50-51324 discloses a method comprising adding an anionic surfactant or an amphoteric surfactant to a developer; J. P. KOKAI No. Sho 55-95946 discloses a method which comprises adding a water-soluble cationic polymer to a developer; and J. P. KOKAI No. Sho 56-142528 discloses a method comprising a water-soluble amphoteric polymeric electrolyte to a developer.
However, if these developers are used in an automatic developing machine for a long time period, there is observed foaming during developing operations. Moreover, if such developers are stored for a long time period after a long term processing, water is evaporated and generation of deposits such as sludge and/or feculence which sometimes result in various troubles such as contamination of lithographic printing plates in an automatic developing machine, clogging of a pump, and so on.